1. Field of the Invention
The present invention relates to tools used in carpentry and in machine work, and particularly to devices for locating the center of surfaces such as squares, circles, etc., as well as for drawing a circle on a surface.
2. Description of the Related Art
It is frequently desirable to locate the center of a surface, for example, in order to center a knob on the square or rectangular face of a drawer front, or in order to punch a hole through the center of a circle made from sheet metal. It is possible to locate the center of such geometric surfaces by making a series of measurements with rulers and dividers, performing a series of arithmetical calculations, and subsequently laying out the required distance with rulers and dividers or compasses and protractors to locate and mark the desired point. However, such methods may not produce an acceptable degree of precision and accuracy, since there may be a number of measurements required, and some degree of error associated with each measurement. In addition, the process can be inconvenient and burdensome, particularly when it must be done repetitively.
It is therefore desirable to have a tool which may be applied to a work surface in order to mark the center of the surface directly without the need for repetitive measurements and calculations. The present invention provides a device for locating the center of circles, squares, rectangles, straight lines, and other surfaces by means of extensible arms operatively connected by a rack and spur gear arrangement. The device may also be used to make measurements, and to draw circles.
A variety of devices have been developed for locating the center of a surface directly without the necessity for performing multiple measurements, reading a scale, or performing calculations. Several devices employ a pair of moveable arms connected by a rack and pinion mechanism. U.S. Pat. No. 794,170, issued Jul. 11, 1905 to J. W. Fessler, describes two strips slidable in opposite directions connected by a pinion, each strip having a jaw at each end of the strip and the pinion having a hole through its axis adapted for receiving a center punch. The device is used for locating center lines. U.S. Pat. No. 1,038,729, issued Sep. 17, 1912 to A. Denes, teaches a tool for finding the center of a circle, the tool having a frame with two pins depending from one end of the frame, a slide mounted on the frame, the slide having a center hole and being connected to a center strip mounted in a slot on the frame and having a least one pin depending from the slide, and a pair of concentric pinions, one engaging a rack on the frame and the other engaging a rack on the center strip. The device is placed on the circle with the three pins abutting the circumference of the circle, the center of the circle being located at the center hole. The device does not locate the center of squares or rectangles.
U.S. Pat. No. 2,599,819, issued Jun. 10, 1952 to S. Fisher, shows a center gage having a base with a gear in the center of the base, two moveable arms having racks defined therein disposed in the base on opposite sides of the gear, work engaging blocks at the ends of the arms, a center hole through the hub of the gear, and a thumbscrew mounted above one of the arms to lock the gear in place. U.S. Pat. No. 2,842,860, issued Jul. 15, 1958 to E. C. Gray, describes a device to center drawer knobs or handles including a bracket for hanging the device from the top edge of a drawer front, three vertical strips with spaced apart holes defined therein, a spur gear mounted to the center of the three strips, and two moveable arms having racks engaging the spur gear, the moveable arms engaging opposite sides of the drawer front. The device essentially only locates the vertical center line of the drawer front.
U.S. Pat. No. 3,628,253, issued Dec. 21, 1971 to W. D. Shepard, teaches a device for marking the center of doorways and other portals having a frame with two slidable members having racks driven by a crank with a main gear and two pinions, the slidable members having marker members with reservoirs for dyes or inks. The doorway is measured, the center of the frame is nailed to the center of the doorway, the crank extends the arms to the edges of the doorways, and a mark is made by pressing down on the marking members. A drawing tool for marking centers on layouts, particularly for use by lithographers, is described in U.S. Pat. No. 3,137,947, issued Jun. 23, 1964 to B. Flower. The device has frame enclosing a pair of movable arms with depending legs, the arms connected by a rack and pinion mechanism, and a pen disposed between the legs.
Devices which use a pair of movable arms connected by a pulley and flexible, continuous loop member include U.S. Pat. No. 3,583,823, issued Jun. 8, 1971 to M. R. Eaton, U.S. Pat. No. 2,928,178, issued Mar. 15, 1960 to S. W. Wilcox, U.S. Pat. No. 4,291,468, issued Sep. 29, 1981 to E. C. Follett, and U.S. Pat. No. 4,326,339, issued Apr. 27, 1982 to C. Marino. Devices to find the center of circles, annular rings, and other round objects are disclosed in U.S. Pat. No. 1,153,149, issued Sep. 7, 1915 to P. Abbott, French Patent No. 7,813,611, published Dec. 7, 1979, and United Kingdom Patent No. 2,093,753, published Sep. 8, 1982.
Other devices include U.S. Pat. No. 1,166,968, issued Jan. 4, 1916 to J. E. Carter (screw with threads in opposite directions); U.S. Pat. No. 1,215,441, issued Feb. 13, 1917 to M. S. Walker (sliding rule for centering headings on typewriters); U.S. Pat. No. 1,703,736, issued Feb. 26, 1929 to A. P. Jacob (beam caliper with rack and pinion mechanism); U.S. Pat. No. 2,559,280, issued Jul. 3, 1951 to H. C. Cochran (arms moved by traverse rod); and U.S. Pat. No. 5,437,105, issued Aug. 1, 1995 to R. H. Work (two crossed arms slidable in two brackets).
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a center locator tool solving the aforementioned problems is desired.